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Page 303
VOLTAGECHART
(Shown from component side)
CIRCUIT DESCRIPTION
This circuit board acts as an automatic switch to increase the
VFO signal injection to the premix circuits on the 28.0 to
29.5
MHz
bands. On the other bands, the VFO signal passes
through the attenuating pad formed by
R1254. R1255, and
R1266.
When the Band switch is turned to any of the four bands in
the 28.0 through 29.5
MHz
range, a positive voltage
is
applied to one of diodes Dl251 through 01254. which
causes
it
to conduct. Consequently, the positive voltage
forward biases
01255, which conducts and permits the
incoming VFO signal to pass through
C1252 to C1254, thus
bypassing the attenuating pad.
In the receive mode, a positive voltage is applied to
tl
of 01251, which
turns on hard and drops its
cc
voltage to a point too low for Dl255 to conduct.
he base
~Ilector
The VFO filter prevents spurious premix products from
entering the receiver injection circuits.
Refer to Page
282
for Schematic symbols.
VFO
RX
10D IOC 108 IOA
IN
CIRCUIT
BOARD
I
I
I
I
I
I
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I
ClP.52
I
RIISI
LIZ51
I
I
I
I
I
I
I
I
I
Dl255
I
I
LIZ32
I
I
I
I
I
I
HFOIPREM
IX
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